This invention generally relates to methods and apparatus for fastening fractured bones and for attaching soft tissue to bone tissue. More particularly, this invention relates to a surgical medical screw having a xe2x80x9cHi-Loxe2x80x9d thread configuration for increasing the pullout strength of the screw, a distal guiding tip for guiding the screw into a pre-drilled implantation site, and a counter-rotation device for resisting loosening of the screw from the implantation site.
Medical screws are commonly used for a variety of surgical procedures. Medical screws may be used as suture anchors to attach a suture to a bone so that the suture may be used to hold soft tissue, such as torn tendons or ligaments, adjacent to the bone. Medical screws may also be used as fastening devices to attach prosthetics such as fixation plates to bone or to join portions of a fractured bone to aid the healing process. The multiple threads of such medical screws improve surgical repair by increasing the xe2x80x9cpullout strengthxe2x80x9d of the screw, that is, the screw""s ability to resist being pulled out from the bone. The threads also reduce the time and force required to implant the screw into the bone.
Various medical screws have been used for attaching objects, such as sutures, plates, or other bone fragments, to bone. U.S. Pat. No. 5,743,914 (Skiba) teaches a bone screw having a head for receiving a screw driving device, a shaft having a first series of helical threads having a first diameter and a first pitch, and second series of helical threads interleaved with said first series of helical threads and having a second diameter and a second pitch, wherein the second diameter is substantially different than the first diameter and at least one of said first and second pitches changes along the length of the shaft. This bone screw exhibits increased pullout strength and is particularly useful for joining bone fragments or for anchoring prosthetics to bone.
U.S. Pat. No. 5,087,201 (Mondani et al.) discloses a self-threading pin which is screw-threaded into the maxilla bone for implantation of a dental prosthetic. The pin has a screw-threaded shank portion, a driving head at one end of the shank portion and a drill bit at the other end of the shank portion. The screw-threaded shank portion of the pin has two intercalated screw threads of different heights.
All of the bone screws disclosed in the prior art generally utilize standard helical thread configurations. The above-described prior art further discloses thread configurations having two different helical threads of different heights interleaved with each other. However, often times these screws are difficult to insert in a pre-tapped/pre-drilled implantation site because there is no guiding mechanism which aids in aligning the screw with the implantation site. Further, the screws of the prior art are apt to counter-rotate, thereby becoming loose from the implantation site.
A medical screw is thus needed which overcomes the shortcomings of the prior art.
A medical screw device according to the present invention addresses many of the shortcomings of the prior art.
In accordance with one aspect of the present invention, a medical screw comprises a head for receiving a screw driving device and a shaft extending from the head. The shaft generally includes respective alternating first and second helical threads running substantially parallel with each other along the shaft (i.e., not intersecting). Additionally, in accordance with the present invention, the second series of helical threads advantageously exhibits a diameter different than the diameter of the first series of helical threads.
In accordance with an alternative embodiment of the present invention, the medical screw may comprise a plurality of series of helical threads, each exhibiting different diameters from the others. In accordance with this embodiment, the plurality of series of threads alternate and run substantially parallel with each other along the screw shaft.
In accordance with another aspect of the present invention, the medical screw may be configured with a variety of different head types and shapes.
In accordance with yet another aspect of the present invention, the medical screw may be manufactured from any type of bio-compatible material, for example, titanium alloy, stainless steel, class six implant grade plastic or a material made from bioabsobables such as polyglycolic acid and the like.
In accordance with yet another aspect of the present invention, the medical screw can exhibit any length, and the diameters of the shaft, the first series of threads and the second series of threads may differ for different types and sizes of the bone in which the screw is to be used.
In accordance with yet another aspect of the present invention, the medical screw comprises a distal guiding tip that aids in the insertion of the screw into a pre-tapped/pre-drilled implantation site in bone tissue.
In accordance with still another aspect of the present invention, the thickness of the first and/or second series of threads decreases along the shaft of the screw.
In accordance with yet another aspect of the present invention, the head of the medical screw comprises at least one eyelet for receiving a suture or multiple sutures.
In accordance with yet another aspect of the present invention, the medical screw comprises counter-rotation mechanisms for resisting loosening of the screw from the implantation site.
In accordance with still another aspect of the present invention, the Hi-Lo thread configuration may comprise a single, contiguous thread changing in height along the shaft of the screw.
These and other aspects of the present invention will become more apparent to those skilled in the art from the following non-limiting detailed description of preferred embodiments of the invention taken with reference to the accompanying figures.